For background information, this patent refers to the following publications,
[Ref-1] xe2x80x9cTCP and Explicit Congestion Notificationxe2x80x9d, Sally Floyd, Lawrence Berkeley Laboratory, Berkeley, Calif. 94704.
[Ref-2] xe2x80x9cOn the Capacity of a Cellular CDMA Systemxe2x80x9d, Gilhousen, et. al., IEEE Transactions on Vehicular Technology, Volume 40, No. May 2, 1991.
[Ref-3] xe2x80x9cErlang Capacity of a Power Controlled CDMA Systemxe2x80x9d, Viterbi, et. al.
1. Field of Invention
The invention relates to control of packet transmissions of various classes of IP/data traffic and obtaining/using capacity estimates from a wireless network. In particular the invention relates to,
1. estimating the available link bandwidth in a wireless network using messages (standard and proprietary) from the wireless network and/or other estimates from an external device, and
2. combining the estimate with priority/class-based control of data packet transmissions to provide an efficient use of available bandwidth (capacity) per cell (sector) on the air interface (wireless link).
2. Description of Prior Art
In order to describe the background of this invention, details on the following two areas need to be presented:
1. Bandwidth management and transmission control in data networks such as IP networks, and
2. Real-time capacity and loading in a wireless network, and the overall network architecture
TCP/IP (Transport Control Protocol/Internet Prototol) is a very well established, widely used standard protocol for data/voice communications over packet networks [REF-1]. TCP handles each connection independently and maintains an end-to-end flow control. As shown in FIG. 1, the sender (103) and the receiver (103) maintain an end-to-end TCP (104) peer relationship. Whereas both the sender and the receiver maintain a IP layer (105) relationship with the router (101). The TCP employs retransmissions and window size control on each data connection making it reliable even when the underlying routing/switching systems experience congestion or temporary failures. The physical layer (100) and layer 2 (106) in such networks can be various standard and/or proprietary methods such as, ethernet, frame relay, ATM, SONET, T1, etc. Though the TCP and IP protocol layers are independent of the lower layers, their performance and efficiency depends on the lower layers.
Several methods of implementing and improving TCP flow control have been developed, but the most basic method is the window-based flow control. When TCP on the receiving machine sends an acknowledgement, it includes a window update in the segment to tell the sender how much buffer space the receiver has available for additional data. The window update specifies the amount of data the receiver can accept beyond the data being acknowledged. The TCP sender sends the amount of data indicated by the window size. The TCP sender also estimates the round trip delay which is used to set/control the TCP window size, which implicitly controls the TCP rate. A window update of zero completely halts the sender transmission. Transmission is resumed upon receiving an acknowledgement with a non-zero window size. In general, the TCP protocol uses the window updates along with other algorithms to control the flow and avoid congestion across the connection.
Current TCP/IP networks rely on packet drops as an indication of congestion. Upon experiencing packet losses, the TCP sender retransmits the lost packet and lowers its window size to reduce the amount of data being sent at a time.
An indirect method to control the data flow of TCP connections is to introduce controllable queues in the transmission path. One such example would be an IP queue in an IP router (101). By queuing (delaying) IP packets, the measured roundtrip delay increases (with potential for TCP timeout), which automatically reduces the TCP window update, thereby lowering the effective TCP data rate. Such methods can be applied to various classes of IP traffic with pre-defined rules. New enhancements include methods to use Explicit Congestion Notification (ECN) [REF-1]. ECN is done by sending a one-bit notification to the sender indicating congestion. The sender TCP then reacts to the ECN bit by lowering the TCP window size to one and initiating a slow-start session.
The TCP window and other capabilities of the TCP/IP protocol provide the necessary capabilities to implement various bandwidth management algorithms.
The other aspect of the background is the wireless network architecture, and the associated capacity and loading. FIG. 2 shows a typical cellular/PCS wireless network and its key components. A typical cellular network (200) covers a contiguous area that is generally broken down by a series of cells (201). Each cell has a base station (202) and may be subdivided into sectors. The base-station maintains a radio link with the mobile station (203) (eg. a cellphone, or a fixed wireless terminal, or a handheld wireless computing device). The other system elements include a Mobile Switching Center (MSC) (205), Base Station Controller (BSC) (204), and a data InterWorking Function (IWF) (206). The data IWF (206) is the entity that provides connectivity of the wireless network (and mobile stations) to the IP/data network via circuit switched and packet switched wireless data protocols.
The cellular network layout provides coverage and serves the mobile and fixed wireless stations with a wireless link to the cells (sectors). The wireless, RF (radio frequency) link to the cells could be based on established industry standards such as IS-54 (TDMAxe2x80x94Time Division Multiple Access), IS-95 (CDMA xe2x80x94Code Division Multiple Access), and GSM (Global System for Mobile Communications), or new upcoming standards such as cdma2000 and WCDMA, or proprietary radio interfaces. Typically a cell (sector) is able to support a certain number of wireless calls. This capacity, number of simultaneous active calls per cell (sector) is a function of (depends on) various factors such as frequency reuse, carrier to interference ratio, bit-energy to noise ratio, effective bit-rate per call (voice or data), frame error rate (FER), etc. Several studies have been done in estimating the air link capacity in a wireless network [Ref-2, Ref-3]. The radio spectrum (frequency band) used in a particular cell (sector) is reused in every xe2x80x9cn xe2x80x9d cells (sectors). For example, in a CDMA (IS-95-based) system, n=1 indicating that the frequency band is being re-used in every cell (sector). In other cellular systems such as GSM and TDMA, xe2x80x9cn xe2x80x9d could be 3, 4 or 7 or any fraction thereof. The frequency reuse factor xe2x80x9cnxe2x80x9d, carrier to interference ratio (C/I), bit energy to noise ratio (Eb/No), processing gain, handoff gain, total time-slots, total frequency channels, total power, expected data rate per user, expected power per user, and engineering specifications (amongst other factors) determine the maximum capacity per cell (sector) that can be supported to ensure service within certain performance metrics. In some systems, such as CDMA (IS-95, W-CDMA, cdma2000), the capacity per cell (sector) indicates a threshold such that the system or call performance degrades below a certain quality of service if the traffic in the cell (sector) exceeds the threshold. Typically cellular/PCS wireless networks are engineered such that the number of simultaneous active calls per cell (sector) is maintained below a certain threshold. This is done to ensure acceptable system and call performance.
Radio spectrum being a limited resource, considerable engineering and technology effort is spent to ensure the most efficient use of the air interface. Fundamentally the air interface capacity per cell (sector) is limited by the data rate (in bits per second) that can be transferred across the air link for a given set of quality (FER) and reuse parameters. Also, well established traffic engineering/planning approaches are used to engineer the cellular networks such that the number of simultaneous active calls, resulting from the random call arrivals and departures, that exceed the capacity threshold is minimized. As mentioned before, the capacity usage of a particular call depends on various factors including the data rate. Typically, for a reasonable voice quality performance, a voice call transmits data at the rate of 8 kbps (kilo bits per second), 13 kbps, or upto 64 kbps depending on certain vocoders used. Wireless data services such as circuit switched data and packet switched data can allow data rates of 8 kbps up to 115 kbps per data call in current CDMA (IS-95), TDMA, and GSM cellular systems. Future extensions of these systems (cdma2000, W-CDMA) would allow upto 2 Mbps (mega bits per second) per data call.
In the current network architecture, the data IWF (206) provides an access/entry point for all IP/data connections to the wireless network. Various IP/data bandwidth management algorithms can be implemented to allocate bandwidth based on application demand (or based on class of traffic). However, the bandwidth control for IP/data connections based on the available localized capacity in the wireless network can not be performed. The data IWF (206), in the current networks, is not aware (or capable of using) the localized air link capacity information. In other words, when the data IWF (206) sends IP data packets to/from the mobile station (203), it may potentially cause significant degradation (or inefficiency) in the localized air interface link. In short, the ability to control IP data transmission (at the TCP (104), IP (105), or lower layers) based on the localized air interface link capacity does not exist.
Accordingly, several objects and advantages of my invention are:
It is an object of the present invention to provide a system and method that combines the process and result of estimating the available capacity on the localized air link with the dynamic and real-time control, throttle, delay and queuing of certain (or all) classes of data traffic transmissions at TCP (104), IP (104), and/or lower layers of the protocol stack.
It is the object of the present invention to improve the overall throughput of a wireless voice/data network.
It is a further object of the present invention to delay, prioritize, and exploit the latency requirements of various classes of traffic by artificially controlling the burstiness of data packet transmissions to maximize the use of available capacity in a particular cell (sector) in the wireless network.
It is another object of the present invention to obtain estimates of the real-time capacity thresholds per cell (sector), and the real-time usage per cell (sector) using control and signaling messages from the wireless network (mobile, BTS, BSC, MSC, IWF).
It is an object of this invention to continually, dynamically improve and refine the capacity threshold estimates and the usage estimates based on various messages from the wireless network (mobile, BTS, BSC, MSC, IWF).
It is yet another object of the present invention to control the IP transmissions based on the real-time feedback provided by the externally estimated localized air link capacity per cell (sector).
It is the object of the present invention to allow different classes of IP data traffic to have different priorities for accessing the wireless network channel which has a varying bandwidth availability. In order to achieve these and other objectives, the present invention provides a system and method which estimates and uses the real-time available localized capacity per cell (sector) to schedule, throttle, delay or queue various classes of IP data traffic.
The present invention evaluates the control/signaling messages in the wireless network to obtain the number of simultaneous active calls in all cells (sectors), and to develop estimates of capacity thresholds, and available bandwidths. The control messages are to be obtained via tapping various interfaces (standard and proprietary) such as A interface (BSC-MSC) (207), L interface (MSC-IWF (208), BSC-IWF (209)), or Abis interface (BTS-BSC (210), BTS-MSC), or are obtained from entities which are an integral part of the MSC, BSC, BTS, mobile station, or any other element of the wireless network.
The present invention allows for obtaining the capacity threshold estimates and bandwidth availability estimates from a unit/device which is external (not an integral part) of the wireless network.
The present invention uses the localized bandwidth estimates obtained to dynamically control the data transmission of various classes of IP applications. The dynamic, real-time control of IP transmissions are via a combination of non-standard and standard bandwidth management methods such as use of TCP window size and IP layer queuing.
The combination of estimating the real-time localized air-interface capacity/bandwidth and using it to throttle, delay, and/or queue IP connections based on various classes of traffic provides a significant performance and capacity enhancement for a wireless data (and voice/data) network.